The present invention relates to an apparatus for palatal expansion with an extension part which can be lengthened and shortened and having a fixation part on both ends.
Such an apparatus, also referred to as distractor, is used in maxillofacial surgery and maxillofacial orthopedics. It allows a gradual, i.e. step-wise and fast extension of the maxilla in its width or to separate two other bone segments gradually in the sense of a distraction away from each other. The apparatus may also be used in widening the maxilla in one step, in order to precisely adjust the position of the two halves of the palate relative to each other and to the mandible during surgery.
In this way congenital or acquired occlusal disturbances, malformations, bone asymmetries and pathologic relations between maxilla and mandible can be corrected.
In the first main application, the so called rapid palatal expansion, the aim is to correct an insufficient width of the maxilla by a maxillofacial surgery and orthopedics treatment such that the relation between maxillary and mandibular dentition is normalized. Thereby, the maxilla consists of a left and a right half which are united in the mid-sagittal plane in the palatal suture. In patients with an age of 12-14 years, this suture is usually not yet ossified to a great extent. Therefore the gradual separation of the two halves of the hard palate allows the orthognathic correction easily. In older juveniles or adult the suture is closed largely to completely. In these cases a surgical intervention is often necessary during which parts or the maxilla are weakened to an extent that the suture may be separated again to subsequently perform the gradual widening.
In the second main application, the conventional distraction of bone segments in an arbitrary direction, the aim is to lengthen bones in directions with insufficient length. A typical example is the too short horizontal part of the mandible which results in an overjet with the corresponding orthodontic complications and the esthetic problems with respect to the facial profile. In a surgical intervention the bone is osteotomized and bridged by the distractor. After a short initial healing phase of some days the callus forming in the osteotomy site is gradually distracted, i.e. the bone segments are moved apart by the distractor.
In a further application, such apparatus are only used during the surgery to precisely position parts of the maxilla relative to each other. A typical example is the correction of a cleft-lip-palate. This precise positioning is very difficult without such an apparatus due to the forces extorted by the soft tissues. After reaching the desired position and after controlling the occlusion with the mandible, the bone segments are fixated in the resulting position and the apparatus is subsequently removed again.
The main group of appliances used today in clinic is that where the appliances are fixated on the dentition. Therefore they have some important disadvantages.
A further option is the supporting on palatal plates. However, with those a precise guidance of the movements is very difficult due to the indirect transmission of forces via the mucosa. Below the pressure areas inflammations and hygienically problems can occur.
Known distractors of the former type which are fixated to the dentition are described for example in EP 0919207 A1, WO 94/26196 and U.S. Pat. No. 3,977,082. Distractors for palatal expansion which are based on palatal plates residing on the palatal mucosa are described in EP 0308645 A1.
Finally, WO 94/10933 describes a distractor which is based on the dentition as well as on palatal plates.
One disadvantage of the paradontal basement is the fact that the two halves of the palate may tilt in the frontal plane with the currently used designs instead of moving apart with a stable angle relation in the frontal view.
A further disadvantage of the presented state of technology is the fact that the currently available appliances enable only a single-axis, parallel displacement of the two halves of the hard palate. In the clinical application, however, it is often required to do a non-parallel widening, for instance where the posterior palate needs more expansion than the anterior. It is also important to note that the need for different vectors in the anterior and posterior palate is often only recognized during the course of treatment, because the resistance is different in the anterior and posterior.
The fixation and basement on the teeth loads the parodont which is holding the teeth in the bone. Under certain circumstances this can lead to root resorptions. Furthermore, an unwanted tilting of the teeth cannot be excluded such that eventually not the hard palate is widened but simply the dentition tilted towards lateral. Indeed, there are indications in the literature that up to 75% of the presumed movement is effectively dental rotation by nature, i.e. that the teeth have tilted or moved toward lateral which carries the danger of exposing the roots or of leading to an open bite. In adult patients with periodontal problems or lost teeth or in juveniles with congenital missing teeth a fixation to the teeth is a priori very problematic since the remaining parodont cannot transfer the forces without being harmed.
The present invention has the object to create a distractor which at least in part avoids the above mentioned disadvantages of known distractors, in particular of those which are based on fixation on the dentition.
This object is achieved by an apparatus for palatal expansion with an extenuation part which can be lengthened and shortened along its main axis and which has on both ends a fixation part characterized in that each fixation part has the form of a single-point bone connection.
By using single-point bone fixations on its extension part, such a distractor avoids palatal plates or fixation based on the dentition which would have the aforementioned disadvantages. Thereby, either special anchorage bone screws are placed through a stab incision in the palatal mucosa or the bone fixation units take the form of pins. Such bone fixation parts may be placed and fixated in more or less arbitrary positions on the bone, independent from the corresponding position of the teeth which by no means are required as fixation base for such extension parts. Also, no specific adaptations to the single patient are required as this is necessary for instance when using palatal plates or the dentition, Finally, it is also possible to fixate two distractors in predefined positions in order to extend specific force vectors to the hard palate during the palatal expansion.
It is also possible to place two independent distractors in the anterior and the posterior hard palat such that by different extension a non-parallel expansion becomes possible. Thereby the distraction axes may be placed in a way that not only a widening but also a lengthening of the palate occurs if this is necessary. In one embodiment, the bone fixation unit may be connected to the extenuation part by an adjustable in its position fixable joint. In this connection between extenuation part and bone support or screw a moment may be transferred if this is necessary by clamping the joint to the fixation unit in the one variation while it remains firm in another variation.
To limit the indention depth of the bone fixation unit into the bone and to distribute the pressure over a larger surface a thickening (enlargement) may be foreseen to limit the impression depth. Such a thickening is of advantage in screw shaped bone fixation units as well as in units with pin form.
Such a thickening which in further embodiments can take the shape of a shoulder or a rim, have the additional advantage that they may grow into the mucosa such that a form locking emerges.
Furthermore this ingrowth has the advantage that the bone fixation part is held in position and cannot drop out.
In one constructive variation of the extension part it consists of at least 3 threaded elements which screwed into each other form two counter-sense threaded pairs where turning the mid-thread element in one or the other direction results in an elongation or shortening of the extension part. Such extension parts may by very simple to elongate or shorten despite of their simple construction. Furthermore the rate of elongation or shortening per turn of the thread may be defined by the thread pitch.
In an alternative construction embodiment, the extension part is built from at least three elements. These three elements are connected with each other, whereby the first element has the form of a tube which encloses in its interior the turnable borne second element. The third element is screwed together with the second element in such a way that by turning the second element in one or the other direction the third element is pulled into or pushed out of the first element and therefore the extension part is elongated or shortened.
A construction of the distractor in a way that the axes of the bone fixation units are offset to the axis of the extension part has the advantage that also the bone fixation units can be preadjusted by corresponding fixation elements or may be readjusted. To enable this, the corresponding clamping unit may be arranged in a solvable and movable connection such that also the contained bone fixation unit can be moved together with the clamping element. In a further variation of the appliance also the clamping element is solvable and movable along the extension unit. Especially in an arrangement with axes of the bone fixation units and the extension part which are offset, a surface to exert pressure may be foreseen on the surface opposite to the actual bone connection. This in order to allow the application of a corresponding tool which could take the form a forceps which is inserted between the two opposite pressure surfaces of the bone fixation units and which can be spread such that the bone fixation units are pressed on both sides into the bone. With this construction, for instance, a rough adaptation to the bone geometry may be done, while the fine adaptation is accomplished by the help of the threads. Such a pressure surface on the bone fixation unit may take the form of a grove in order to avoid a slippage of the engaged tool.
Preferentially the joint which connects the bone fixation unit to the extension part takes the form of a ball joint, whereby the ball of the joint is part of the bone fixation unit while the extension part features a corresponding cup to receive this ball and to hold and clamp it. Mainly such a ball joint which may remain turnable or fixated by clamping in the socket enables an adaptation of the distractor such that the bone fixation units do not only move apart in a linear fashion. In one variation the ball joint between the bone fixation and the extension part is not tightened respectively temporarily released which allows the bone segments to adjust their relative angle. This, for instance, will allow the joint heads of the temporomandibular joint (TMJ) to remain in the joint socket during a mandibular midline distraction which will avoid the onset of problems in the patient""s TMJs.
The previously mentioned clamping elements can be constructed such that the form one threaded element of the extension part. Thereby the corresponding threaded element of the clamping unit may be a tube with interior thread into which a threaded rod is screwed.
Further details of the invention become apparent from the following description of different design variations and the corresponding drawings.